Method of preparing paving material



Patented May 2, 1933 GLENN H. ALVEY, OF SAN ANTONIO, TEXAS, ASSIGNOR TOUVALDE ROCK ASPHALT COMPANY, OF SAN ANTONIO, TEXAS, A CORPORATION OFTEXAS METHOD OF PREPARING PAVING MATERIAL No Drawing.

This invention relates to a new and improved rock asphaltpavingmaterial' and -method of preparing the same, and more particularlyto such a, paving materlal ncluding as an ingredlent lnnestonecontaining substantially no bitumen. 2

Limestone rock asphalt or rock asphalt occurs in nature and is found inscattered deposits in different parts of the world. It

comprises a pure limestone base of a porous, fossiliferous character,mostly shell, more or less thoroughly and intimately impregnated withasphalt. The asphalt in thisrock is approximately pure and, due to theporous character of thelimestone, the lighter distillates of the bitumenhave passed. off in the ages since its formation, leaving a hardbitumen. The said too]: asphalt, as it is found in the United States,'isparticularly adapted to withstand wear of traflic and weather conditionswhen properly prepared and installed in place. I I

In consideration of my invention it must be recognized that limestonerock asphalt is a natural product and differs widely in physicalanalysis from an artificial asphalt paving material or a sandstone rockasphalt, which have approximately the same chemicalv analysis. Thisdifference betweenthe limestone rock asphalt and the artificial pavingmaterial or the sandstone rock asphalt is clearly indicated in the factthat the asphalt is contained within each particle in the formermaterial, and is a coating on the outside of each particle in thetwo'latter materials.

In the construction ofasphalt pavements or surfacing, it has been foundadvisable to'so govern the penetration of the asphaltic content by meansof fluxing or hardening agents, that the finished product falls withincertain specified limits calculated to enable the material to providesatisfactory service within the range of the temperature extremescontemplated during the life of the pavement. In the construction ofpavements or surfacing with limestone rockasphalt, it has been foundthat the material may be installed either hot or cold, but with eitherprocess it, is necessary to introduce from petroleum. This fact is truewhen the impregnating Application filed October 13, 1930. Serial No.488,556.

a fluxing agent to increase the penetration of the asphalt content so asto softenthe asphalt andthereby prevent cracking, as the natural stateofthe asphalt is too-hard and brittle to perform satisfactory serviceunless softened with asphaltic oils or various commercial fluxes. Theseoils contain a sufficient amount of solvents to enable 1 them toamalgamate with the hard native asphalt thereby softening it to theproper consistency. The commercial fluxes have been made to amalgamatewith the hard native asphalt either through the use of heat or avolatile solvent added as the two are mixed together. 7

- The results obtained with limestone rock asphalt pavements laid underthe various processes used at present have been mostly good, but at thesame time-thesepavements have often been too hard or brittle, and areespecially subject to cracking if there is any yield whatsoever in thefoundation.

Many such pavements arenot soft enough to flow under the pressure oftrafiic and .high summer temperatures so I as to heal up the cracks thatmight develop due to rapid change in temperature or displacements in thefoundations. 7 g

The pure asphaltscontained in thenative limestone rock asphalts isalmost invariably a very high grade pure bitumen that hasa remarkabledegree of stability and can withstand the weathering action of theelements much better than can asphalt manufactured. particularly bitumenis hard like the asphalt in the rock asphalts produced in Uvalde County,Texas. These hard native bitumens are especially useful in themanufacturefof high gradepaints, 9'0 moulding compounds, waterproofing.compounds andmineral rubber, and consequently sell for a relatively highprice as; compared to asphalt derived from petroleum. Under presentcompetitive conditions, however, it has not been commercially possibleto extract the asphalt from theserock asphalts due principally to thefact that approximately ten tons of material have to .be

'paratus into two parts;

asphalt, and there remains as waste nine tons of soft porous limestonewhich has practically no commercial value. In other words, the one tonof pure asphalt has to bear the entire. cost incident to the mining,preparation, and handling of ten tons of rock asphalt, as well as thecost of the extraction process. On the other hand, if it were possibleto provide a ready market for the waste porous limestone, the extractionof pure asphalt from rock asphalt would be entirely feasible andcommercially profitable.

It is' an object of the present invention to provide a paving mixtureand method of making the same, which mixture is flexible and pliablewhen laid and used.

' It is a further object to provide a mixture and method in whichlimestone rock asphalt from which the asphalt has been removed, servesas an ingredient.

s It is an additional object to provide a method and mixture whichincludes the removal of the natural hard bitumen from part of the rockasphalt and the substitution therefor of a softer bitumen or asphalt.

Other and further objects will appear as the description proceeds.

- In making my improved paving mixture I use fine ground waste porouslimestone and a soft asphalt as the matrix of my paving mixture, toprovide flexibility and pliability, and I use rock asphalt as the largerparticles to give strength and long wearing qualities to the pavementmade from this mixture.

In preparing this composition I pulverize the limestone rock asphalt t0the proper and predetermined size suitable for the work for which thepaving mixture is being made. Ordinarily I would crush the rock asphaltand down, using a swing hammer pulverizer or other crushing equipmentthat would tend to cause the large and small particles to be in suchproportions as to form what is generally known as a balanced grading. Ithen separate this pulverized rock asphalt by the use of screens orother ap- (1) relatively fine material and (2) relativelycoarse'material. The relatively fine material (comprising from 20 to 50%of the whole when pulverized 4 and down) will be of such size that 95%will pass a 20 mesh screen; The relatively coarse material comprisingapproximately 40 to 80% of the whole, will be of such size that 95% willbe retained on-a 40 mesh screen.

I then take the relatively fine material and extract the pure hardasphalt from it by means of a suitable solvent or combination ofsolvents in conjunction with the proper equipment designed for thatpurpose. After the extraction there remains a finely porous limestonedue to the fact that the asphalt which formerly occupied these pores hasbeen removed.

I next incorporate in this finely porous limestone a relatively softasphalt in sufficient quantity to fill all the voids or pores and toprovide a thin film of asphalt on the surface. There are several ways inwhich this may be done, namely (1) by heating until fluid the softasphalt; (2) by cutting back the soft asphalt with a solvent; or (3)emulsifying the asphalt in water and mixing same with the porouslimestone. I prefer the emulsion process as there is no danger ofoverheating, and it is much cheaper than the use of solvents My nextstep is to add the relatively coarse rock asphalt to this fine porousmaterial which has been treated with soft asphalt and mix the twothoroughly together.

Finally,for thepurpose of coating the rockasphalt particles, I add anadditional quantity of soft asphalt which has been emulsified with wateror, if preferred, which has been cut back with a solvent. In some casesI may use a commercial fiux or even an asphaltic base flux oil. Exceptin the case of the emulsified asphalt,.I also add a small quantity ofwater so as to prevent the mixture from setting up and getting hardbefore it is used. I

If I want a non-skid paving mixture I add approximately 20% of finelycrushed trap rock or other sharp rock harder than the rock asphalt. I

Owing to the fact that there are so many variables in this mixture it ispractically impossible to set even approximate limits to the amounts ofeach ingredient used, or to give the exact mixing procedure, but inorder that one familiar with the art of making asphalt paving mixturemay manufacture a product such as herein described, I give below oneformula which has proven successful Solid ingredients 80% porouslimestone from which hard asphalt has been extracted (100% passing 40mesh) 1 50% limestone rock asphalt (100% passing 4 and retained on 40mesh); v

20% trap rock (100% passing A and retained on 40 mesh). 1

- U Liquid ingredients Asphalt emulsion (50% water and 50% soft asphalt)being in amount of 8% of the solid ingredients. I

Order 0 f mixing put in the emulsion until the whole has become ahomogeneous mass.

The material thus prepared will form a pavement or asphalt surface thathas a high stability, excellent wearing ualities, and comparatively highdegree of fexibility and pliability. It will be noted that the principaland very important difference between this composition and the rockasphalt mixtures generally in use now is that the cementing medium ofthe latter is an amalgamation of the pure native bitumen and roadoil orfiux whereas the cementing medium of the former is almost entirely thesoft asphalt which was introduced into the fine porous limestone. Thisis true because there will be a relatively small amount of the soft asphalt that will amalgamate with the hard native asphalt inasmuch asthere are relaquantity of soft asphalt to coat the coarser rock asphaltmaterial.

5. The process for the manufacture of a rock asphalt paving mixturewhich comprises crushing rock asphalt, separating the finely crushedmaterial from the coarser material, removing the natural asphalt fromthe finely crushed material, adding to the finely crushed material afterextraction of tively few surfaces of-contact between the two asphalts,whereas in mixture designed according to present day practice theasphaltic oil or flux is intimately in contact with the native bitumenand it is heated or solvents are used so as to force an amalgamation ofthe two.

I contemplate such changes and modifica- V tions of my mixture and themethod of preparing it as may come within the spirit and scope of theappended claims.

I claim:

1. The process for the manufacture of a rock asphalt paving mixturewhich comprises crushing rock asphalt, removing the natural asphalt froma portion of the crushed material, and adding a soft asphalt asa binder.

2. The process for the manufacture of a rock asphalt paving mixturewhich comprises crushing rock asphalt, removing the natural asphalt froma portion of the crushed material, and adding a soft asphalt in anemulsion with water as a binder.

3. The process for the manufacture of a rock asphalt paving mixturewhich comprises crushing rock asphalt, separating the finely crushedmaterial from the coarser material, removing the natural asphalt fromthe finely crushed material, adding to the finely crushed material afterextraction of the natural asphalt a soft asphalt in an emulsion withwater to form a binder, and finally adding tothe mix the coarser rockasphalt material.

4:. The process for the manufacture of a rock asphalt paving mixturewhich comprises crushing rock asphalt, separating the.

finely crushed material from the coarser material, removing the naturalasphalt from the finely crushed material, adding to the finely crushedmaterial after extraction of the natural asphalt a soft asphalt in anemulsion with water to form a binder, adding to the mix the coarser rockasphalt material, and finally adding an additional

